Linear RF transmitters are known. A Cartesian feedback transmitter constitutes one such known transmitter. When properly adjusted, such a negative feedback based transmitter architecture will operate in a satisfactory linear mode.
The loop in the amplifier in a Cartesian feedback transmitter must be open at times, such as when the transmitter is powered up or when phase training is performed. Upon restoring the closed loop operation, however, the loop gain must be ramped up slowly in order to prevent splatter, where splatter typically results from RF energy radiated at frequencies other than those assigned to the transmitter. In addition, the gain must be increased to the full amount in a limited amount of time. Conversely, when the loop is opened, the loop gain must be ramped down slowly to prevent splatter. In this case, the gain must be reduced to a substantially zero value in a limited amount of time.
Accordingly, there is a need for an apparatus for a linear amplifier that ramps up or down the loop gain slowly to prevent splatter, but which completes the gain ramping process within a limited amount of time.